Induction heating cooking devices have been widely used as providing advantages, such as safety, cleanness, and high efficiency, and applied for use in home or commercial kitchens.
Japanese Patent Laid-Open Publication No. 61-292832 discloses a conventional touch key of capacitance detecting type. This touch key includes a flat panel and electrodes provided on both surfaces of the panel to form a capacitor. The change of the static capacitance of the capacitor caused by the touch of one electrode with a finger is converted into the change of a direct current (DC) voltage.
Japanese Patent Laid-Open Publication No. 2005-85667 discloses another conventional induction heating cooking device including a touch key of static capacitance detecting type. This cooking device includes plural touch keys of static capacitance detecting type and a controller for receiving signals from the touch keys. The controller receives the signals successively while being synchronized with a commercial power supply, and changes the order of the signals to be received at a predetermined interval. This operation allows the controller to detect that the touch keys are close to a cooking pan without being affected by leaking magnetic field.
In these conventional touch keys of static capacitance detecting type may erroneously start or stop heating operation as if the touch keys are activated by a finger when a user spills water on the keys or when cooked material is boiled over from a cooking pan onto the keys.